1. Field of the Invention
The present invention relates to an apparatus for a liquid crystal display (LCD) device, and more particularly, to a liquid crystal drop apparatus, which is capable of finely adjusting the amount of liquid crystal dropped on a substrate of the LCD device, and a method for dropping liquid crystal using the same.
2. Discussion of the Related Art
In general, the LCD device has a lot of advantages, such as a low operating voltage, a low power consumption rate, realization of full colors, a light weight, a thin profile, and miniaturization. For this reason, the LCD devices have been widely applied to various fields, from a clock, a calculator, a monitor for PCs, and a notebook computer to a TV, an aeronautical monitor, a mobile terminal, and a portable phone. A typical LCD device includes an LCD panel for displaying an image and a circuit unit for driving the LCD panel. The LCD panel further includes a first substrate having a TFT array formed thereon, a second substrate having a color filter array formed thereon, and a liquid crystal layer formed between the first and second substrates.
On the first substrate of the LCD panel, a plurality of gate lines are arranged at regular intervals in one direction, and a plurality of data lines are arranged at regular intervals in a direction vertical to the gate lines, thereby defining pixel regions. Moreover, a plurality of pixel electrodes are formed in the pixel regions for displaying an image. A plurality of TFTs are formed in the pixel regions at the intersections between the gate lines and the data lines, and are switched on/off by driving signals of the gate lines for transferring image signals of the data lines to the pixel electrodes. On the second substrate of the LCD panel, a black matrix layer is formed for blocking light at portions except for the pixel regions, and an R, G, and B color filter layer is formed at portions corresponding to the pixel regions for expressing colors. Moreover, a common electrode is formed on the entire surface of the second substrate including the color filter layer. In an In Plane Switching (IPS) mode liquid crystal display device, the common electrode may be formed on the first substrate. The first and second substrates are bonded to each other with a designated space formed therebetween, and the liquid crystal layer is formed in the designated space.
Typically, the liquid crystal layer is formed by either a liquid crystal injection method or a liquid crystal drop method according to the related art. A process for manufacturing the LCD panel is varied in the related art methods. FIG. 1 is an exploded perspective view schematically illustrating an LCD device according to the related art. As shown in FIG. 1, the related art LCD device includes a lower substrate 1 and an upper substrate 2, which are bonded to each other with a designated space formed therebetween, and a liquid crystal layer 3 injected into the designated space between the lower substrate 1 and the upper substrate 2.
Specifically, on the lower substrate 1, a plurality of gate lines 4 are arranged at regular intervals in one direction and a plurality of data lines 5 are arranged at regular intervals in a direction vertical to the gate lines 4, thereby defining pixel regions (P). Moreover, a plurality of pixel electrodes 6 are formed in the pixel regions (P) in which the gate lines 4 and the data lines 5 intersect each other, and a plurality of TFTs (T) are formed at the intersections between the gate lines 4 and the data lines 5. On the upper substrate 2, a black matrix layer 7 is formed for blocking light at portions except for the pixel regions (P), an R, G, and B color filter layer (not shown) is formed for expressing colors, and a common electrode 9 is formed for forming an image.
Although not shown in FIG. 1, each of the TFTs (T) further includes a gate electrode protruded from the gate line 4, a gate insulating film formed on the entire surface of the lower substrate 1, an active layer formed on the gate insulating film on the upper portion of the gate electrode, a source electrode protruded from the data line 5, and a drain electrode opposite to the source electrode. The pixel electrodes 6 may be made of a transparent conductive metal with a high transmittance, such as Indium-Tin-Oxide (ITO).
In the above-described related art LCD device, the liquid crystal layer 3 located on the pixel electrodes 6 is oriented by signals applied from the TFTs (T), and the amount of light transmitted by the liquid crystal is adjusted by the degree of the orientation of the liquid crystal layer 3, thereby displaying an image on the LCD device.
FIG. 2 is a flow chart schematically illustrating a method for manufacturing an LCD device using the liquid crystal injection method according to the related art. As shown in FIG. 2, a TFT array is formed on a first substrate at Step 1S, and a color filter array (not shown) is formed on a second substrate at Step 5S. After that, at Steps 2S and 6S, orientation films for orienting liquid crystal are respectively formed on the first substrate and the second substrate, and are rubbed. Then, at Steps 3S and 7S, the first substrate and the second substrate are respectively washed. Thus, the first and second substrates are bonded to each other such that spacers for maintaining a cell gap for an LCD panel are dispersed on the first substrate at Step 4S, and Ag for connecting common lines with the common electrode and a sealant for bonding the first and second substrates are applied to the edge of the second substrate at Step 8S. Here, the applied sealant is patterned with a liquid crystal inlet.
At Step 9S, the first and second substrates are transferred into a bonding apparatus to complete the bonding of the first and second substrates. Thereafter, at Step 10S, the bonded first and second substrates are loaded in a hardening furnace (not shown) to harden the sealant. After the hardening of the sealant is completed, the bonded first and second substrates are cut into unit LCD panels by scribing and breaking processes at Step 11S. Thus, at Step 12S, the liquid crystal is injected into a space between the first and second substrate of each unit LCD panel through the liquid crystal inlet in a vacuum chamber, and then the liquid crystal inlet is sealed. Specifically, when the liquid crystal inlet is soaked in a liquid crystal solution under the condition that the space between the bonded first and second substrates is in a vacuum state, the liquid crystal is injected into the space due to an osmotic action. After the liquid crystal is injected into the space between the first and second substrate, the liquid crystal inlet is sealed using a sealant. Finally, the unit liquid crystal display panels are tested, and sent out at Step 13S.
In the related art liquid crystal injection method, since the liquid crystal inlet is soaked in the liquid crystal solution under the condition that the vacuum state in the space between the bonded first and second substrates is maintained, it is time-consuming to inject the liquid crystal, thereby deteriorating productivity. Moreover, when the liquid crystal is injected into the space between the bonded first and second substrates to manufacture a large-sized LCD panel, it is difficult to completely inject the liquid crystal into the large-sized LCD panel, thereby resulting in a poor quality LCD panel. For this reason, the LCD panels for portable phones or PDA phones are manufactured by the liquid injection method, whereas the large-sized LCD panels are manufactured by the liquid crystal drop method.
Hereinafter, a method for manufacturing an LCD device using the liquid crystal drop method according to the related art will be described. FIG. 3 is a flow chart schematically illustrating the related art method for manufacturing the LCD device using the liquid crystal drop method. As shown in FIG. 3, a TFT array is formed on a first substrate at Step 21S, and a color filter array is formed on a second substrate at Step 25S. Then, at Steps 22S and 26S, orientation films for orienting liquid crystal are respectively formed on the first substrate and the second substrate, and are rubbed. After that, the first substrate and the second substrate are respectively washed at Steps 23S and 27S. Thus, at Step 24S, an adequate amount of the liquid crystal is dropped on the first substrate such that the liquid crystal is dropped at central portions of respective liquid crystal panel regions, without contacting a sealant until the sealant is completely hardened to maintain a cell gap. On the other hand, at Step 28S, the sealant and Ag balls are dispensed on the edges of the respective liquid crystal panel regions of the second substrates. Here, the sealant is independently patterned in the liquid crystal panel regions. At Step 36S, spacers are dispersed on the first substrate, on which the liquid crystal is dropped.
After that, at Step 29S, the first and second substrates are transferred into a vacuum bonding chamber (not shown), and are bonded to each other in the vacuum bonding chamber. Specifically, the second substrate is reversed so that the surface of the second substrate on which the sealant is deposited faces down, and is mounted on an upper stage of the vacuum bonding chamber, and the first substrate on which the liquid crystal is dropped is mounted on a lower stage of the vacuum bonding chamber. Then, the vacuum bonding chamber is evacuated to create a vacuum so that the first and second substrates are bonded to each other.
At Step 30S, the thus-bonded first and second substrates are loaded from the vacuum bonding chamber to a UV hardening furnace (not shown), and the sealant is hardened therein by irradiating UV rays onto the sealant. Specifically, a mask (not shown) having a light shading film is used on portions of the first and second substrates except for portions to which the sealant is applied, and the sealant is thus hardened by irradiating the UV rays onto the sealant. Further, at Step 31S, the bonded first and second substrates are loaded in a thermal hardening furnace, and the sealant is thermally hardened. At this time, the liquid crystal dropped on respective liquid crystal panels is spread.
After the UV hardening and the thermal hardening of the sealant are completed, the bonded first and second substrates are cut into unit liquid crystal display panels at Step 32S. Then, the unit liquid crystal display panels are polished at Step 33S, tested at Step 34S, and sent out at Step 35S.
As described above, the related art liquid crystal drop method can save time by dropping the liquid crystal on the substrate, thereby improving productivity and remedying the deficiencies caused by the incomplete injection of the liquid crystal into a large-sized LCD device.
FIG. 4 is a schematic view of a liquid crystal drop apparatus according to the related art. As shown in FIG. 4, the related art liquid crystal drop apparatus includes a liquid crystal container 20 filled with liquid crystal 10, and a nozzle 30 connected to a lower end of the liquid crystal container 20 for dropping the liquid crystal 10 of the liquid crystal container 20.
Specifically, when nitrogen (N2) gas is supplied to the liquid crystal container 20, a pressure of the nitrogen gas causes the liquid crystal 10 of the liquid crystal container 20 to be dropped on a substrate through the nozzle 30. The size of the liquid crystal drops on the substrate is determined by the surface tension of the liquid crystal 10 and the influence of gravity, and is adjusted by vertically moving the liquid crystal drop apparatus or changing the shape of the nozzle 30. In order to adequately display an image on the LCD device, it is necessary to precisely drop an adequate amount of the liquid crystal. However, since the surface tension of the liquid crystal 10 dropped from the nozzle 30 is determined by physical properties of the liquid crystal 10, the adjustment of the size of the liquid crystal drops by the related art methods is limited.